1-to-1 Relationship Fields for Carbon Fields

related_post_field.php

<?php
namespace Carbon_Fields\Field;

use Carbon_Fields\Exception\Incorrect_Syntax_Exception;

/**
* Taxonomy field class.
*/
class Related_Post_Field extends Select_Field
{
    protected $post_type = array();

	/**
	* Stores the post type as an array
	*
	* @var array|string
	**/
    public function set_post_type( $post_type ) {
        if ( ! is_array( $post_type ) ) {
            $post_type = array( $post_type );
        }

        $this->post_type = $post_type;
        return $this;
    }

    /**
    * Get posts for each post type passed to field type
    *
    * @return array $posts The selectable options of the relationship field.
    */
    private function options_for_post_type($post_type)
    {
        $filter_name = 'carbon_relationship_options_' . $this->get_name() . '_post_' . $post_type;

        $args = apply_filters( $filter_name, array(
            'post_type' => $post_type,
            'posts_per_page' => -1,
            'fields' => 'ids',
            'suppress_filters' => false,
        ));

        return array_reduce(get_posts($args), function(&$result, $id) {
            $result[$id] = $this->get_title_by_type( $id, 'post', $post_type );
            return $result;
        });
    }

    /**
    * Generate the item options for the select field.
    *
    * @return array $options The selectable options.
    */
    protected function load_options() {
        $options = array();

        foreach ( $this->post_type as $post_type ) {
            $options = array_merge( $options, $this->options_for_post_type($post_type) );
        }

        $this->options = $options;
    }

    /**
    * Used to get the title of an item.
    *
    * Can be overriden or extended by the `carbon_relationship_title` filter.
    *
    * @param int     $id      The database ID of the item.
    * @param string  $type    Item type (post, term, user, comment, or a custom one).
    * @param string  $subtype The subtype - "page", "post", "category", etc.
    * @return string $title The title of the item.
    */
    public function get_title_by_type( $id, $type, $subtype = '' ) {
        $title = get_the_title( $id );

        if ( ! $title ) {
            $title = '(no title) - ID: ' . $id;
        }

        /**
        * Filter the title of the relationship item.
        *
        * @param string $title   The unfiltered item title.
        * @param string $name    Name of the relationship field.
        * @param int    $id      The database ID of the item.
        * @param string $type    Item type (post, term, user, comment, or a custom one).
        * @param string $subtype Subtype - "page", "post", "category", etc.
        */
        return apply_filters( 'carbon_relationship_title', $title, $this->get_name(), $id, $type, $subtype );
    }
}

taxonomy_field.php

<?php
namespace Carbon_Fields\Field;

use Carbon_Fields\Exception\Incorrect_Syntax_Exception;

/**
 * Taxonomy field class.
 */
class Taxonomy_Field extends Select_Field
{
    protected $taxonomy;

    /**
     * Stores the taxonomy for the dropdown
     *
     * @var string
     **/
    public function set_taxonomy($taxonomy)
    {
        if ( taxonomy_exists($taxonomy) ) {
            $this->min = $this->add_options($this->values_for_taxonomy($taxonomy));
        } else {
            Incorrect_Syntax_Exception::raise('Only valid taxonomies are allowed in the <code>set_taxonomy()</code> method.');
        }

        return $this;
    }

    private function values_for_taxonomy($taxonomy)
    {
        $terms = get_terms(array('taxonomy' => $taxonomy, 'hide_empty' => false));

        return array_reduce($terms, function(&$result, $item) {
            $result[$item->term_id] = $item->name;
            return $result;
        });
    }
}